The aim of this work is the development of a multibody model of a quadrotor helicopter system in presence of wind fields by using Simscape Multibody Environment. The simplified model of the quadrotor is modelled as a non linear system which is under-actuated and strongly coupled. For the dynamics, aerodynamic effect of drag, the thrust due to the rotation of propellers and external wind fields are considered. In particular, a study on the evaluation of the thrust coefficients is conducted. Thrust evaluation, for prescribed trajectories, gives us indications about the type of propellers and motor characteristics to be installed on the UAV.